This invention relates generally to cable systems which involve horizontal and vertical lifelines. More particularly, the present invention relates to cable systems which protect workers by means of connecting the worker with a safety cable.
Safety cable systems in the form of horizontal lifelines have been employed for a number of years to provide fall protection for workers on elevated structures. Conventional safety systems involve a lanyard which connects with a safety harness or a safety belt worn by the worker. The lanyard attaches to the cable and slides along the cable as the worker moves about the structure.
The most advantageous use of the horizontal lifeline occurs when the lifeline is sufficiently taut that the lifeline can also function as a steady rail for the worker. However, when the cable is sufficiently taut that the cable assumes a linear or substantially linear configuration, the resistance force magnitude required to effectively withstand the load impact of a falling worker becomes theoretically exceedingly large. In the event of a fall, the construction worker ordinarily generates many times his weight in the impact force exerted by the connector of the lanyard against the cable. Accordingly, the cable, the cable anchorage and/or the supporting structure are highly susceptible to failure. Any of the noted failures are antithetical to the central safety purpose of any safety cable system.
In order to ensure that the safety cable systems function for their intended results, i.e., to provide fall protection for the worker, governmental and regulatory agencies have implemented various standards. For example, a common regulatory standard requires that the anchorage for the cable be capable of withstanding at least 5,400 pounds. These latter minimal standards are often difficult to achieve and can be wholly impractical in the field because the required cable is quite heavy and very few portions of buildings, concrete, framework or scaffold are capable of supporting the minimum anchorage force during the construction phase.
In summary, general considerations dictate that in order to effectively decelerate a falling worker, a substantial resistance force must be exerted at the end of the lanyard. The resistance force is preferably exerted by an initially taut horizontal lifeline which remains taut after an initial sag has been imparted to the lifeline upon impact.